Drop Build prefix and settle on Lib and Exe prefixes. Also add a
note about the "else" part of the condition and fix offenders.
While at it, define COND_LIB_SAL_TEXTENC to be used by sal to
prevent diverting coditions in build and cxx code.
Change-Id: I944587ca1ccbe46b765d1a631a7214c8126fe951
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/128136
Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>
